Meter Stick Lab

The objective of this lab was to use a meter stick and a 100g lead weight to find the mass of the meter stick. My original plan was to find the lever arm of the meter stick with the weight and than calculate the torque by using the equation torque = lever arm x force. My plan did not work because I did not know that the force that had to be used for this equation was only the force of the lead weight and not the force of the lead weight plus the force of the meter stick as I previously thought. When me and my partner started to try different approaches to finding out the mass of the meter stick we both agree that the torque of the meter stick would equal the torque of the lead weight. (torque1 = torque 2 /  force x lever arm = force x lever arm) since the meter stick was balancing. From that point we started to try finding the numbers that had to be plug in to find the weight of the meter stick. We knew that force in this case would equal the weight of the meter stick and the other force would equal the weight of the lead weight.  We balanced the meter stick with the lead weight on the edge and found that the lever arm for the that side was 29 cm and assumed that the lever arm for the meter stick alone would be from the axis of rotation to the end of the stick (51 cm). Thinking we finally got the right result we wrote down the equation: 

           

This was not the right result! After struggling some more we noticed that the force could not be in grams therefore the force had to be converted to newtons. We used the formula w = mg and found out that the force was 0.98 Newtons. That was not our only mistake on the equation above. Miss Lawrence explained that the lever arm for the the meter stick was not 51 because that was not the measure from the center of mass of the meter stick to the axis of rotation. To find the correct lever arm we balanced the stick without the weight and than measured the distance between the distance from the axis of rotation of the system to the center of mass of the stick and we got 21.2 cm. Now that we had all the correct number we plug them all in the previous equation:

                

When I got to this result and converted from weight to mass (w = mg) and got 0.136 I though I got the wrong answer again since a meter stick could not be 0.136 grams. Ms. Lawrence than pointed out that my answer was not in grams but in Kg so it was actually 136g  which makes a lot more sense.